Phase diagram of a QED-cavity array coupled via a N-type level scheme

*Correspondence: [email protected] 1NEST, Scuola Normale Superiore and Istituto di Nanoscienze, CNR, Piazza dei Cavalieri, 7, Pisa, 56126, Italy Full list of author information is available at the end of the article Abstract We study the zero-temperature phase diagram of a one-dimensional array of QED cavities where, besides the single-photon hopping, an additional coupling between neighboring cavities is mediated by an N-type four-level system. By varying the relative strength of the various couplings, the array is shown to exhibit a variety of quantum phases including a polaritonic Mott insulator, a density-wave and a superfluid phase. Our results have been obtained by means of numerical density-matrix renormalization group calculations. The phase diagram was obtained by analyzing the energy gaps for the polaritons, as well as through a study of two-point correlation functions.